How to create an embedded document that follows a model with Mongoose? - node.js

Question

I have two models, Post and Comment:
My Post model (models/post.js):
var mongoose = require('mongoose');
var Comment = require('../models/comment');
var Schema = mongoose.Schema;
module.exports = mongoose.model('Post', new Schema({
text: {type: String, trim: true},
postedBy: String,
comments: [Comment]
}));
My Comment model (models/comment.js):
var mongoose = require('mongoose');
var Schema = mongoose.Schema;
module.exports = mongoose.model('Comment', new Schema({
user: String,
comment: {type: String, trim: true},
created: {type: Date, default: Date.now(), select: false}
}));
When I attempt to create a new post without any comments, the post is created perfectly fine.
Although when I try to $push a comment to the post after creation, nothing happens.
Post.findOneAndUpdate(
{"_id": req.params.id},
{$push: {comments: {
comment: "Hello World",
user: "933ujrfn393r"
}}
}).exec(function(err, post) {
console.log(post);
res.json({success: true});
});
Why is this failing to push the comment to the post? My console.log(post) line simply logs undefined, so not too sure what is happening here. I tried a simple test of Post.findOne({"_id": req.params.id}) and it returned the post successfully, so there is no problem with the find query.

Answer 1

Embedded sub documents
Your usage implies an embedded sub document inside the model which only requires a schema definition for the sub document. This will store both schema's in a single document in a single collection in MongoDB
var mongoose = require('mongoose');
var Schema = mongoose.Schema;
var CommentSchema = new Schema({
user: String,
comment: {type: String, trim: true},
created: {type: Date, default: Date.now(), select: false}
});
var PostSchema = new Schema({
text: {type: String, trim: true},
postedBy: String,
comments: [CommentSchema]
});
module.exports = mongoose.model('Post', PostSchema);
Then create comments as you were.
Post.findOneAndUpdate(
{"_id": req.params.id},
{$push: {comments: {
comment: "Hello World",
user: "933ujrfn393r"
}}
}).then(function (post) {
console.log(post);
res.json({success: true});
});
Document references
If you want to keep the two models then you would need to use a reference in your Post schema instead. This will create seperate documents in seperate collections in MongoDB and use the _id to look up the second document.
var PostSchema = new Schema({
text: {type: String, trim: true},
postedBy: String,
comments: {
type: mongoose.Schema.Types.ObjectId,
ref: 'Comment'
}
});
Then comments need to be created before you can reference them in the Post model.
c = new Comment({ comment: 'x' })
c.save().then(function (result) {
return Post.findOneAndUpdate(
{ _id: req.params.id },
{ $push: { comments: result._id } }
);
}).then(function (result) {
console.log('updated post');
});
Population can be used to easily retrieve the "foreign" documents.

Answer 2

Based on this question, I believe your problem is that you're embedding the Comment Model instead of the Comment Schema.
Try changing post.js from:
var Comment = require('../models/comment');
to:
var Comment = require('../models/comment').schema;
This also makes sense after looking at the example on the Mongoose docs regarding sub-docs.
P.S.
What helped me investigate this was outputting the err object of the exec callback to see what was actually going on...